A Study on Wire Ball/Pad Open Failure Mechanism of a Multi-Stack Package (MSP) under High Temperature Storage (HTS) Condition

The mechanism of a wire ball/pad open failure at a gold wire and bonding pad interface of a multi-stack package (MSP) under high temperature storage (HTS) condition, 150 degC, is studied. Failure analysis using FE-SEM (field emission) and FIB-SEM (focused ion beam) was conducted. The analysis revealed that the main factors that contribute to a ball/pad failure were the tensile (pull-off) stress imposed on the gold wire and the bond weakening process due to metallic diffusion and corrosion. By preparing altered MSP samples and conducting verification HTS tests, it was found that the tensile stress was due to the thermal expansion of the protective encapsulant applied at the wirebonding region. Further failure analysis using FIB-SEM, AES, and TOF-SIMS indicated that the bonding strength between the gold wire and pad degraded due to the Kirkendall void resulting from metallic diffusion at high temperature and the IMC corrosion due to ion impurity